package com.mftour.common.utils;

import java.util.Date;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * 分布式ID生成器
 * @author minimu
 *
 */
public class SeqGen{
	private static SeqGen sgInst = null;
	private static AtomicBoolean lock = new AtomicBoolean(false);
	
	private final static long twepoch = 1288834974657L;
	// 机器标识位数
	private final static long workerIdBits = 7L;
	// 数据中心标识位数
	private final static long datacenterIdBits = 3L;
	// 机器ID最大值
	private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
	// 数据中心ID最大值
	private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
	// 毫秒内自增位
	private final static long sequenceBits = 12L;
	// 机器ID偏左移12位
	private final static long workerIdShift = sequenceBits;
	// 数据中心ID左移17位
	private final static long datacenterIdShift = sequenceBits + workerIdBits;
	// 时间毫秒左移22位
	private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

	private final static long sequenceMask = -1L ^ (-1L << sequenceBits);

	private static long lastTimestamp = -1L;

	private long sequence = 0L;
	private long workerId = 0;
	private long datacenterId = 0;
	public static SeqGen getInstance(long workerId, long datacenterId){
		while(lock.get()){
			try {
				Thread.currentThread().sleep(1);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		lock.set(true);
		if(null==sgInst){
			sgInst = new SeqGen(workerId,datacenterId);
		}
		lock.set(false);
		return sgInst;
	}

	/**
	 * 生成全局唯一ID工具类
	 * @param workerId 服务器ID
	 * @param datacenterId 应用ID
	 */
	 private SeqGen(long workerId, long datacenterId) { 
		if (workerId > maxWorkerId || workerId < 0) { 
			throw new IllegalArgumentException("worker Id can't be greater than %d or less than 0"); 
		} 
		if (datacenterId > maxDatacenterId || datacenterId < 0) { 
			throw new IllegalArgumentException("datacenter Id can't be greater than %d or less than 0"); 
		} 
		this.workerId = workerId; 
		this.datacenterId = datacenterId; 
	}

	public synchronized long nextId() {
		long timestamp = timeGen();
		if (timestamp < lastTimestamp) {
			try {
				throw new Exception("Clock moved backwards.  Refusing to generate id for " + (lastTimestamp - timestamp)
						+ " milliseconds");
			} catch (Exception e) {
				e.printStackTrace();
			}
		}

		if (lastTimestamp == timestamp) {
			// 当前毫秒内，则+1
			sequence = (sequence + 1) & sequenceMask;
			if (sequence == 0) {
				// 当前毫秒内计数满了，则等待下一秒
				timestamp = tilNextMillis(lastTimestamp);
			}
		} else {
			sequence = 0;
		}
		lastTimestamp = timestamp;
		// ID偏移组合生成最终的ID，并返回ID
		long nextId = ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift)
				| (workerId << workerIdShift) | sequence;

		return nextId;
	}

	private long tilNextMillis(final long lastTimestamp) {
		long timestamp = this.timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = this.timeGen();
		}
		return timestamp;
	}

	private long timeGen() {
		return System.currentTimeMillis();
	}
	
	public static void main(String[] args) {
		/*
		SeqGen sg = new SeqGen(1L,2L);
		for(int i=0;i<100000;i++)
			System.out.println(i+","+System.currentTimeMillis()+":"+sg.nextId());*/
		//Object o = "abc";
		long start = System.currentTimeMillis();
		int count = 1000;
		for(int i=0;i<count;i++)
			SeqGen.getInstance(1L, 2L).nextId();
		long spend = System.currentTimeMillis()-start;
		System.out.println(spend+"ms:"+count+","+count/spend+"条／ms");
		
		System.out.println(-1L ^ (-1L << 7));
		
		Date date = new Date(1288834974657L);
		System.out.println(date);
	}
}
